This invention relates to surgical instruments, and particularly to the so-called "box lock" instruments. Instruments such as forceps, hemostats, and clamps are often provided with box lock joints particularly where a high degree of reliability and the very accurate meeting of grasping members is required.
The box lock joint is a special hinge used in instruments of the type comprising first and second members each having, at one end, operative means such as a clamping or gripping jaw adapted to cooperate with the operative means of the other member, and each having at its opposite end manipulable means, typically a ring handle, for controlling the movement of the operative means on the same member. The first member has a bifurcated portion at an intermediate location whereby its operative means and its manipulable means are connected to two separate elements having a slot between them. The second member extends through the slot with its operative means and its manipulable means on opposite sides of the bifurcated portion of the first member. A pin, extending across the slot and through a hole in the portion of the second member within the slot, completes the hinge and allows the operative means to be controlled by the manipulable means for clamping, depending on the nature of the particular instrument. The box lock joint is generally preferred because of its strength, the low degree of play which it allows, and its resistance to working loose. These characteristics are of particular importance in special instruments wherein the accurate cooperation of opposed operative means is required. This is the case, for example, with surgical clamping means having jaws specially designed to clamp tubular vessels of the body with the avoidance of damage thereto such as those described in U.S. Pat. No. 3,608,554, issued Sept. 28, 1971.
Heretofore, forceps and other surgical instruments having box lock joints were typically made by producing aligned holes in the two members to be joined, inserting a temporary pin, performing the necessary bending operations as well as grinding and polishing operations, removing the temporary pin, punching the holes in the bifurcated portion of the first member to a square or star configuration, hardening the first and second members, inserting a second pin, swaging or peening the pin, and finally finishing the instrument. Swaging of the pin following hardening results in the setting up of stresses in the instrument which remain unrelieved when the instrument goes into use. When the instrument is subjected to the influences of superheated steam (autoclaving), repeated mechanical loads under surgical conditions, and corrosion caused by the various elements in the surgical environment, these stresses eventually, if not in a very short time, manifest themselves as cracks in and around the box lock joint. Instrument breakage often occurs at the location of these cracks, and can constitute a serious safety hazard if it takes place during surgery.
In some cases, the hinge pin is inserted and swaged prior to hardening. However, peening is sometimes required to tighten the pin when shrinkage occurs in the hardening process. This peening results in stresses similar to those which occur when the pin is swaged following hardening. The danger of breakage therefore exists in instruments made by this alternative method.
The hinge pin itself is also susceptible to breakage. Although it is not a common occurrence, if a hinge pin in a conventional instrument breaks, it is possible for a part of the pin to fall out of the instrument while in use. In surgery, such an occurrence also represents a serious hazard to the patient's safety. In accordance with this invention, a pin having a head slightly larger than the holes in the member having the bifurcated portion is inserted into the aligned holes in the two members. The pin is electrically fused in two steps, and thereby secured to the two separate elements of the bifurcated portion, there being a circular zone of fusion in each of the two separate elements having a penetration depth desirably between 75 and 100 percent and preferably 100 percent. Fusion preferably takes place in an inert gas environment. The outer surfaces of the two separate elements of the bifurcated portion are ground and polished, and the pin becomes invisible. Hardening takes place after electric fusion. The process produces a substantially stress-free box lock joint which is much less likely to fail in use than box lock joints made in accordance with conventional methods. In addition, if the hinge pin fractures, it is prevented from falling out of the instrument by the fact that it is fused to the elements of the bifurcated portion of the first member.
The principal object of the invention, therefore, is to provide a substantially stress-free box lock joint having greater durability than conventional box lock joints. A second object of the invention is to insure against the loss of the hinge pin or parts thereof in the event of hinge pin breakage. Further objects of the invention include the simplification of the manufacturing process and the production of a box lock joint having as little play as possible. Still other objects will be apparent from the following detailed description when read in conjunction with the drawings.